1. Field of the Invention
Exemplary aspects of the present invention generally relate to an image forming apparatus, such as a copier, a facsimile machine, a printer, or a multi-functional system including a combination thereof, and more particularly, to an optical writing unit that forms an electrostatic latent image on an image bearing member and an image forming apparatus including the optical writing unit.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile capabilities, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image bearing member (which may, for example, be a photoconductive drum); an optical writing unit projects a light beam onto the charged surface of the image bearing member to form an electrostatic latent image on the image bearing member according to the image data; a developing device supplies toner to the electrostatic latent image formed on the image bearing member to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image bearing member onto a recording medium or is indirectly transferred from the image bearing member onto a recording medium via an intermediate transfer member; a cleaning device then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the unfixed toner image to fix the unfixed toner image on the recording medium, thus forming the image on the recording medium.
Tandem-type image forming apparatuses are known for forming a multi-color image. Generally, such tandem-type image forming apparatuses are equipped with an optical writing unit that illuminates and scans a plurality of photosensitive members serving as latent image bearing members for different colors arranged in tandem with light beams based on image information. Accordingly, latent images are formed on the surface of the photosensitive members. The latent images are developed with respective colors of development agents such as toner into toner images or visible images. Subsequently, the toner images are transferred onto a transfer member such that they are superimposed one atop the other, thereby forming a composite toner image on the transfer member.
The transfer member may be a belt-type transfer member and a recording medium that directly contacts the photosensitive drums. When using a belt as an intermediate transfer member (hereinafter referred to simply as an intermediate transfer belt), the latent images formed on the photosensitive members are transferred onto the intermediate transfer belt such that they are superimposed one atop the other, forming a composite toner image on the intermediate transfer belt in a process known as a primary transfer process. Subsequently, the composite toner image is secondarily transferred onto a recording medium in a process known as a secondary transfer process.
After the composite toner image is transferred onto the recording medium, the composite toner image is fused and pressed onto the recording medium so that the composite toner image is fixed thereon. After the image is fixed on the recording medium, the recording medium is discharged outside the image forming apparatus.
There is demand for a low-priced and compact image forming apparatus while it provides high imaging quality. In order to achieve high imaging quality, generally, misalignment of toner images, also known as color drift, needs to be prevented by adjusting the position of the light beams projected from the optical writing unit relative to the surface of the photosensitive members. Adjustment of the light beams on the photosensitive drums involves adjustment of the orientation of a long-length lens (such as a toroidal lens) mounted in the optical writing unit.
In a known approach, a color drift detector is provided in the image forming apparatus to detect color drift of images, and in accordance with a detection result, a motor in the optical writing unit is driven to physically change the orientation of the long-length lens, hence adjusting the position of the light beams arriving at the surface of the photosensitive drums. Instead of using the motor, the alignment of the long-length lens may be changed manually.
In another approach for adjustment of the orientation of the long-length lens, the orientation of the long-length lens such a deflecting mirror is adjusted using a jig during manufacture and then fixed to the optical writing unit. In this approach, an additional device for adjustment is not required, thereby providing a low-priced and compact image forming apparatus. However, once color drift occurs, the orientation of the long-length lens or the mirror is difficult to adjust, resulting in degradation of imaging quality.
Alternatively, the image may be corrected using software controlled by a controller and electric control.
In recent years, with the advancement of molding technology for resins, the lens used in the optical writing unit can have a relatively complicated lens surface. Furthermore, in order to shorten a lead time for the molding process, the lens is becoming thinner and smaller. Such a lens can satisfy various performance, but is easily deformed by an external force, resulting in degradation of a beam diameter on the photosensitive members.
If the lens is fixed to the optical writing unit, the desired performance can be achieved reliably. However, when changing the orientation of the lens to correct the beam position on the photosensitive members to correct color drift, the lens gets deformed undesirably, worsening the beam diameter.
To address such a difficulty, upon adjustment of the long-length lens, a contact point of the long-length lens is moved by an adjustment motor, and a spring member such as a leaf spring presses the long-length lens against the contact point to enable the lens to follow the contact point. In another technique, a holder is attached to the long-length lens for reinforcement, and the long-length lens is moved together with the holder.
Although advantageous, if the spring member such as the leaf spring has strong elasticity, the long-length lens that focuses the light beam deflected by the deflector onto a scan target is deformed, and/or the pressure of the spring member exceeds the drive force of the adjustment motor, preventing the light beam from striking a desired position of the photosensitive members and achieving a desired performance. For this reason, the elastic member presses the lens with a minimum required pressure.
There is a drawback in such a optical writing unit in that the contact point and the support point of the focusing lens and a housing of the optical writing unit are easily moved by vibrations, shock, and heat during transportation.
In view of the above, there is thus an unsolved need for an optical writing unit capable of preventing displacement of a lens due to shock and heat while allowing easy adjustment of color drift.